Using a sharp knife, poke several 1 inch deep holes in the roast. Insert the garlic slivers into the holes.
In a small bowl, combine the paprika, celery salt, garlic powder, parsley, ground black pepper, chili powder, cayenne pepper, seasoned salt, mustard powder, and dried tarragon; mix together well and rub over the meat.
In a separate small bowl, combine the beer OR cola, Worcestershire sauce, hot pepper sauce and liquid smoke and mix well. Place the roast in a slow cooker and pour this mixture over the meat.
Add the onion, green bell pepper and jalapeno chile peppers to the slow cooker.
Cook on low setting for 10 hours, or more, if desired.